This invention relates generally to the soldering art and, more particularly, to an apparatus for soldering at least one elongated conductor to a plurality of solar cells to establish electrical connection between the cells.
In recent years, substantial effort has been expended to develop automated equipment for the assembly of solar panels. In the course of these efforts, it has proved difficult to design a machine capable of rapidly and accurately interconnecting individual solar cells into a string. For example, a solar panel soldering apparatus is described in Bycer, "Automated Solar Module Assembly Line: Final Report", Department of Energy Publication No. DOE/JPL/ 955287-80/6, August 1980. The Bycer apparatus involves a "walking beam conveyer" for moving and indexing solar cells through various stations before they are transferred to a conveyor belt for final soldering. The walking beam conveyor individually picks up cells from one station and swings forward to advance them to the next station for performance of a subsequent operation. After advancement, a cell is held at the new station by vacuum and the conveyor mechanism retracts to its initial position. The indexing system is controlled by a microprocessor and serves to advance the cells through a number of stations, including a flux application station and a first soldering station at which a pair of short conductive tabs are connected to the upper surface of each cell. Upon reaching the conveyor belt, each cell is inverted and positioned for connection with a string of preceding cells. The cell is connected to the string from above by soldering the tabs to the opposite surface of the preceding cell. The string of soldered cells then progresses intermittently along the conveyor belt through at least one additional station. The cells are supported on the conveyor belt by tapered support wheels arranged in groups of four to engage the cells at isolated points thereabout. The soldering operations are performed by induction heating or pulsed heating.
Another soldering apparatus is disclosed in Somberg, "Automated Solar Panel Assembly Line: Final Report", Department of Energy Publication No. DOE/JPL-955278-81, May 1981. In the Somberg machine, cells are connected in series by segments of copper ribbon driven downwardly between two adjacent cells and forwardly under the first of the cells, causing a leading end of each segment to contact the underside of the first cell. The trailing end of the segment is then allowed to fall over and contact the opposite side of the succeeding cell. To accomplish this, ribbon from a storage reel is first driven at a rapid rate and then advanced more slowly over the top of the succeeding cell, whereupon it is sheared to produce a discrete ribbon segment. The segment is soldered to the cells in this configuration by a heat lamp and a pair of pincher rollers downstream of the ribbon feed location.
In the Somberg apparatus, a complex ram mechanism pushes each cell intermittently through a number of different process stations and finally onto a conveyor belt for transport to a soldering station. The ram advances each cell from a handling cassette to a "standby" position, and from the standby position to a "ribbon feed" position at which the conductive ribbon is fed behind and beneath the cell. The cell is then picked up by the conveyor belt, allowing the trailing end of the ribbon to fall on the succeeding cell.
The functions of the Somberg apparatus are implemented sequentially by proximity sensors which produce discrete control signals in response to a metallic coating at the edges of the cells. The pincher rollers are driven at the speed of the conveyor belt and each cell is held by a plurality of spring loaded arms which snap inwardly to captivate the cell.
As seen from the above discussion, the machines of Bycer and Somberg are rather complex and difficult to control. The walking beam conveyor of Bycer has a large number of moving parts which must operate with great precision to maintain cell alignment. The conveyor inverts the cells at a crucial point between soldering operations and intermittently moves them down the assembly line. Such movement can be highly disruptive of cell alignment. The Somberg machine is also complex and has inherent problems of cell alignment, ribbon feed and machine timing. For example, the ram mechanism and the snap-in arms tend to torque the cells from their intended positions, the ribbon feed mechanism can jam, and the proximity sensors used for timing are unreliable.
Therefore, in many applications it is desirable to provide a relatively simple and inexpensive apparatus for connecting solar cells in series by at least one conductive element.